Radio transmission apparatuses based on a pulse scheme are utilized for radio transmission systems of ultrawide band (UWB) which includes a microwave band and a quasi-millimeter wave band.
In the pulse radio transmission apparatus, a base-band signal outputted from a base-band signal generator is converted into a pulse by a pulse generator. In addition, the pulse is band-limited and is turned into a wave packet by a band-pass filter. Subsequently, the wave packet is amplified by a transmission amplifier, and the wave packet is transmitted from an antenna through a transmission/reception changeover switch (RF switch). On the other hand, a signal received by the antenna is amplified by a reception amplifier through the transmission/reception changeover switch. In addition, the signal is band-limited by a band-pass filter, the signal is detected by a wave detector, such as envelope detector, and a base-band signal is regenerated by a base-band signal regenerator.
As compared with a narrow-band communication scheme, such a pulse scheme has a feature that an oscillator or a mixer is unnecessary, so the RF section becomes simple in configuration and low in cost. Thus, the radio transmission of a wide band exceeding 10 Gbps may be realized in a millimeter wave band for which a wide band can be utilized.
The configuration of a transmission apparatus in a pulse radio transmission apparatus disclosed in JP-A-2006-303705 is illustrated in FIG. 10A, while the operation of the transmission apparatus is illustrated in FIG. 10B. In the configuration, a rectangular wave signal (a pulse signal) generated by an XOR circuit by delaying a clock signal is applied to a transmission signal generation unit, and is modulated with a data signal so as to be outputted as a transmission signal. An RF switch (reference numeral 35 in FIG. 10A) for turning ON/OFF the RF pulse signal with the data signal is employed for the transmission signal generation unit. If a frequency band which the pulse radio transmission apparatus uses is, for example, a microwave band, problems may be slight. However, when the frequency band becomes a millimeter wave band exceeding 30 GHz, wide-band and high-speed switching characteristics are required of the RF switch. However, the wide-band and high-speed RF switch is very expensive and is large, thus causing the problem that the transmission apparatus will be large in size and high in a fabrication cost.